Geometrical Isomerism (Animated)

SINHA’s I. I.T. CHEMISTRY

-1-

Problem solving skill to find no of structural isomers . In general, the students find it difficult to identify the no of isomers for any given molecular formula. Here is a more convenient and systematic approach developed by S.K.Sinha ,kota (India). Step 1: Find the index of Hydrogen deficiency using the Formula For any compound with molecular formula CnHmClxOyNz

where n==no of carbon m=no of hydrogen x= no of monovalent atoms like F,Cl, Br,I, D ,T etc y= no of divalent like O z= no of trivalent like N.

2n+2-m-x+z I

Ex.

=

Where I = index of hydrogen deficiency

For C6H6 I=(6X2+2-6)/2 =8/2 =4.

Here I is the sum of total no of cycles(rings) Step -2 Write all possible carbon sleletons for given formula. CH3

Ex C4H10

CH3 H3C

& H3C

CH3 H3C

CH3

Ex C5H12

H3C

CH3

H3C CH3

H3C

CH3

CH3

CH3

Ex C6H14

H3 C

CH3 H3C

H3C

CH3 CH3

CH3 CH3

CH3 H3C

CH3 CH3 H3C

H3 C CH3

1-D-10 Talwandi & B-7. JAWAHAR NAGAR, KOTA.(RAJ) Ph-0744-2422383 .Mo-93149-05055

SINHA’s I. I.T. CHEMISTRY

-2-

Step-3 :-Find all possible functional group for the given molecular formula using index of hydrogen deficiency. Ex C3H6O here index =(2X3+2-6)/2 =1 Index 1 means 1 pi bond or one cycles. Let there is 1 Pi bond 1. pi with c=c then O must be as --OH or --OR OH OH

CH3

H2C a

H2C

CH3 HO

b

CH3 H2C

c

O

d

here b & C are unstable as they are enol and not counted as isomers. 2 . pi with c=O then C must be as ------R O O H3C H3C

a

CH3

b H

Let there is one cycle . The cycle may be with carbon only as cyclopropane , Or the cycle may include O also as below. O

O CH3 a

c

b

4 Arrange all possible functional groups on all possible carbon chains.and remove the structures with unstable functional groups.For above given problem the total structural isomers possible are ………………….. OH H2C

CH3 H2C

a

O

O H3C

O b H3C

OH

c

d H

CH3

O

O

e

f

CH3 g

1-D-10 Talwandi & B-7. JAWAHAR NAGAR, KOTA.(RAJ) Ph-0744-2422383 .Mo-93149-05055